Commercial aircraft require a fresh air supply. This air can be provided by various sources such as an engine compressor, an auxiliary power unit (“APU”) or other sources. It is common practice to supply environmental control systems in larger aircraft with bleed air from aircraft engines. Air-conditioning units of popular aircraft environmental control systems comprise one or more large-volume heat exchangers, through which ram air flows during the flight. The ram air is used for cooling the bleed air. The ram air is usually supplied through ram air ducts. Relatively modern commercial aircraft are provided with environmental control systems that can be operated without or with relatively little bleed air. In order to provide the relatively large air quantities required for pressurizing, ventilating and air-conditioning the cabin, it is practical to utilize relatively large fresh air inlets on the fuselage of the aircraft. Such fresh air inlets usually extend outward from an outer contour of the aircraft fuselage and have, for example, a curved, scoop-like shape that is also referred to as “ram air scoop” or “ram air inlet scoop.”
The shape of this type of fresh air inlets is designed for the cruising state that by far represents the longest flight phase, particularly for long-range commercial aircraft. In these flight phases, a relatively high speed of, for example, 0.8 Ma is reached such that a pronounced ram pressure is generated at the fresh air inlets despite the low air density at cruising altitude. The air flowing into an air duct arranged behind the fresh air inlet due to the ram pressure is preferably compressed further with the aid of a compressor in order to increase the air pressure to the value required for pressurizing the cabin and fed into a downstream network of ducts, from where it can be routed into the corresponding air treatment systems. In order to fulfill the specified acoustic requirements during ground operations—a certain air speed should, in particular, not be exceeded—and to minimize the pressure loss so as to save energy, it may be required to install one or more secondary air inlets that provide additional inflow cross sections on the ground in order to thusly reduce the flow resistance and to lower the average flow speed. However, the operation of these secondary air inlets requires mechanically actuated flaps or shutters that seal the secondary air inlets during the flight.
In the use of the above-described fresh air inlets, it is furthermore disadvantageous that these fresh air inlets need to be protected from dust and small objects being swirled around during operating phases near the ground, wherein this is usually realized with a deflector shield. This deflector shield is arranged, for example, in a pivoted fashion upstream of the fresh air inlet referred to the flow direction and able to absorb the kinetic energy of the foreign matter. This additional mechanical device increases the complexity of such a fresh air inlet system.
It is the object of the invention to propose a fresh air inlet for an aircraft that has the lowest complexity possible, a low weight and the fewest movable parts possible and ensures a sufficient supply of fresh air for an environmental control system of an aircraft that essentially operates without bleed air during flight and ground operations, namely with the lowest possible power demand of a downstream compressor.
This object is attained with a fresh air inlet for an aircraft that features at least one ram air inlet with at least one ram air inlet opening, at least one secondary air inlet opening that is spaced apart from the ram air inlet and at least one movably mounted flap, wherein the flap can be moved into a first position and into a second position, and wherein the flap essentially covers the secondary air inlet opening in the first position and at least partially opens the secondary air inlet opening and at least in certain areas extends into the air flow directed toward the ram air inlet opening in order to shield the ram air inlet opening from foreign matter in the second position.
In the fresh air inlet according to the invention, a deflector shield required for the ram air inlet is realized in the form of the flap that simultaneously serves for covering another secondary air inlet opening. The first position of the flap is assumed in flight phases, in which a relatively high flying speed is reached and the aircraft is located far above the ground. The secondary air inlet opening could be realized, for example, in the form of an opening that is located directly in an outer surface of the aircraft. This opening could be arranged, in particular, in an area on the underside of the aircraft fuselage, wherein it would be possible to realize, for example, an opening in the fairing of the wing-fuselage transition (“belly fairing”). In order to cover the secondary air inlet opening, the flap fits tightly against the edges of the secondary air inlet opening such that a largely smooth, continuous surface is created when the secondary air inlet opening is closed. In this case, the ram air inlet is not impaired by the flap such that the entire surface of the ram air inlet opening is available for taking in ram air.
In the second position of the flap, the secondary air inlet opening is not covered by the flap such that the entire secondary air inlet opening is available for taking an air from the surroundings. When the aircraft is on the ground and the environmental control system is switched on, air can be taken in from the surroundings through the secondary air inlet opening, as well as through the ram air inlet, and used by the environmental control system. In this context, it needs to be observed that the flap should be positioned at a sufficient distance from the ram air inlet such that no or only minimal fluidic influences occur between the secondary air inlet opening and the ram air inlet during ground operations. At slow speeds such as, for example, during takeoffs and landings of the aircraft, a considerably enlarged inlet opening for ambient air is also available for the ram air inlet due to the combination of a secondary air inlet flap and a deflector shield according to the invention.
The fresh air inlet according to the invention has a number of advantages in comparison with fresh air inlets known from the prior art. On the one hand, the pressure loss of the fresh air inlet can be reduced due to the increased cross-sectional surface on the ground or in flight phases with relatively slow speed. This results in a considerably lower energy expenditure for any downstream compressors or blowers. In addition, the intensity of flow-induced noises is reduced due to the more favorable flow characteristics. It is furthermore particularly preferred to essentially design the ram air inlet such that it is only used while cruising. Consequently, it is not necessary to make any compromises that would deteriorate the flow characteristics while cruising for the benefit of ground operations.
In one advantageous embodiment of the fresh air inlet according to the invention, the secondary air inlet opening is situated upstream of the ram air inlet. This favorably affects the simultaneous use of the flap as a cover for the secondary air inlet opening and as a deflector shield for the ram air inlet. This results from the fact that an upstream secondary air inlet opening is passed by the surrounding air flow first such that a flap for closing the secondary air inlet opening that is arranged in the vicinity of the secondary air inlet opening can be easily extended into the air flow flowing directly to the ram air inlet.
In an advantageous additional development of the invention, the flap is essentially located upstream of the ram air inlet and the secondary air inlet opening in its second position. This means that the entire air inlet surface between the flap and the ram air inlet is made available on the ground and the influence of the ram pressure on the secondary air inlet opening is minimized at slow speeds. This likewise makes it possible to realize a relatively large distance between the flap and the ram air inlet opening such that less fluidic interference effects occur at the ram air inlet.
In another advantageous additional development of the air inlet according to the invention, the flap is essentially located between the ram air inlet and the secondary air inlet opening in its second position. This makes it possible to reduce fluidic interferences between the air introduced into the secondary air inlet opening and the air flowing into the ram air inlet opening. In this case, it is particularly practical to adapt the flap to the shape of the ram air inlet because this could favorably affect a shorter distance of the flap from the ram air inlet and a reduced influence on the flow such that the secondary air inlet opening could also be positioned relatively close in front of the ram air inlet in order to reduce the flow resistances of downstream air ducts. Another favorable effect of this arrangement is described further below with reference to another advantageous additional development.
A preferred embodiment of the fresh air inlet according to the invention furthermore features a secondary air inlet duct that is connected to the secondary air inlet opening, as well as a ram air inlet duct that is connected to the ram air inlet opening and a fresh air duct, wherein the secondary air inlet duct and the ram air inlet duct can be connected to the fresh air duct. This makes it possible to combine the flows in the secondary air inlet opening and the ram air inlet such that the entire air taken in from the surroundings is available in a common fresh air duct and can be withdrawn, for example, by an environmental control system of the aircraft.
It is furthermore preferred that the flap can be moved into a third position, in which the flap at least partially extends into the air flow in order to route ram air into the secondary air inlet opening from a surface of the aircraft and at the same time essentially not impair the air flow that is directed toward the ram air inlet opening. Due to this constellation that is favorably affected, in particular, by a flap arranged between the secondary air inlet opening and the ram air inlet, an additional mass flow can be generated in certain flight phases and routed into the secondary air inlet opening in flight by means of the ram pressure. In this operating mode of the air inlet according to the invention, the flap is opened just so far that it does not yet impair the air flow directed toward the ram air inlet opening, but already protrudes into the air flow by such a distance that a clearly noticeable mass flow induced by the ram pressure is introduced into the secondary air inlet opening. This operating mode is referred to as “boost mode” below.
It is furthermore advantageous if the fresh air inlet according to the invention features a check valve that is arranged in the secondary air inlet duct. This makes it possible to prevent the air flow taken in through the ram air inlet from flowing back into the surroundings of the aircraft through the secondary air inlet opening due to the relatively high ram pressure at the ram air inlet, particularly when the secondary air inlet opening is closed. Since the secondary air inlet opening is merely subjected to the static ambient pressure but the ram air inlet opening is subjected to the dynamic ram pressure, a concise pressure differential would form between the two openings and could only be compensated with a very strong suction effect in the fresh air duct if no check valve would be provided.
It is furthermore preferred that the cross-sectional surface of the fresh air duct is at least identical to the sum of the cross-sectional surfaces of the secondary air inlet duct and the ram air inlet duct. This prevents the mass flow flowing into the fresh air duct from being subjected to an increased flow resistance and pressure peaks or vibration effects from occurring at the inlet of the fresh air duct.
In one particularly preferred embodiment of the air inlet according to the invention, an emergency ventilation duct is provided and can be connected to the secondary air inlet duct. In this way, it is possible to create or boost an emergency ventilation system that allows an emergency ventilation of the cabin on the basis of ram air being taken in. This leads to an additional reduction of the weight. The combination of secondary air inlet opening, ram air inlet and emergency ram air inlet is particularly advantageous when the flap is in its third position and additional ram air from the surroundings is also available through the secondary air inlet opening
It is furthermore particularly advantageous if a movably mounted emergency ventilation inlet flap is arranged in the emergency ventilation duct and deactivates the emergency ventilation through the secondary air inlet opening and the ram air inlet during the normal operation of the aircraft, wherein this emergency ventilation can, however, be reactivated on demand by opening the emergency ventilation inlet flap.
It is also preferred that the air inlet according to the invention furthermore features an actuator for moving the emergency ventilation inlet flap in order to open or close the connection between the emergency ventilation duct and the secondary air inlet duct. This would make it possible to automatically open the emergency ventilation inlet flap at the push of a button or automatically with a suitable controller or control unit.
In an advantageous embodiment of the fresh air inlet according to the invention, a compressor for conveying air is located in the fresh air duct. The compressor is primarily required for compressing the fresh air due to the differential pressure of about 0.5 bar or more between the surroundings of the aircraft and the cabin while cruising, as well as the ducts and air treatment systems that create an additional flow resistance. Since the entire inlet opening surface of the secondary air inlet opening and the ram air inlet opening is available, the compressor can have a relatively low power demand in comparison with the prior art because the flow resistance is clearly reduced due to the relatively large inlet opening surface.
It is furthermore advantageous if the flap is pivotably mounted on a hinge. This is particularly simple with respect to mechanical considerations and can be realized with numerous commercially available, perfected and low-maintenance components.
It is also particularly advantageous if the fresh air inlet according to the invention features an actuator for moving the flap that may be realized in the form of an electric, hydraulic or pneumatic actuator. This actuator could be positioned in the immediate vicinity of the flap and reduces the expenditures for mechanical actuating elements.
It is ultimately also advantageous if the fresh air duct, the ram air inlet duct and/or the secondary air inlet duct is designed for accommodating at least one heat exchanger. In this way, the need for additional structural space and the expenditures for integrating a heat exchanger of the environmental control system or other systems can be eliminated. This measure is primarily suitable for relatively small systems that do not impair the main function of the fresh air inlet and for which the air flow provided in the respective duct suffices.
The objective is ultimately also attained with the use of a fresh air inlet according to the above-described characteristics in an aircraft. The objective is furthermore attained with an aircraft with at least one above-described fresh air inlet according to the invention.